I. Field of the Invention
The present invention relates generally to the field of solvent recovery devices. More particularly, the present invention relates to a device and method for recovering a solvent utilized in photopolymer plate processing operations.
II. Description of the Related Art
It is known in the prior art to produce printing plates from acrylic elastomer resins and synthetic rubbers utilizing photoengraving and chemical milling techniques. Generally, a layer of such resins or rubbers are placed onto a surface of a flexible plate and then exposed to light through a photographic film or stencil having a desired pattern to be formed onto the printing plate. Exposure of the resins and rubbers to light cures the resins and rubbers, altering the susceptibility of the resins and rubbers to removal by a photopolymer solvent. By applying the photopolymer solvent to the light exposed layer of resins or rubbers on the printing plate, the uncured photopolymer resin or rubber is chemically etched away by the photopolymer solvent in a pattern reverse to that of the film or stencil. The resin or rubber etched from the plate is removed with the waste photopolymer fluid.
Typically, the solvents utilized for the photopolymer solvent are relatively costly and generally have flash point temperatures above 140xc2x0 F., defining the photopolymer solvent as a Class III liquid in accordance with 29 CFR 1910.106(a)(18)(ii). Further, disposal of the waste photopolymer fluid is likewise relatively expensive and presents environmental problems and concerns. Therefore, to more efficiently produce the aforementioned printing plates, devices were developed to recover the photopolymer solvent from the waste photopolymer fluid.
Prior art photopolymer solvent recovery devices utilize vacuum assisted distillation to separate the photopolymer solvent from the photopolymer resins or rubbers. Upon separation and removal of the photopolymer solvent, the residue resins or rubbers remain in the device as a concentrated residue. Typically, the residue is removed from the device by gravity flow through a drain. One problem with this device is that recovery of the photopolymer solvent is limited. To maintain fluidity of the concentrated residue, a certain amount of photopolymer washout fluid must remain in the residue, otherwise the resins or rubbers will coalesce into an amorphous solid within the device. Once the solid is formed, the device can not be operated until the operator enters and manually removes the solid from the device. This is undesirable because it is both time-consuming and exposes the operator to the chemicals comprising the waste photopolymer fluid. Further, it has been discovered that the concentrated residue has a flash point temperature between 100 and 140xc2x0 F., defining the residue as Class II liquid in accordance with 29 CFR 1910.106(a)(18)(i). Not only is the residue a potential fire hazard, particularly as the residue is drained from the device at an elevated temperature, its disposal is subject to special handling requirements which increase disposal expenses, as compared to a Class III liquid.
In the photopolymer solvent recovery industry, efforts to date are directed to maintaining residue fluidity while maximizing solvent recovery. These efforts resulted in the development of a device utilizing a surrogate solvent to maintain residue fluidity. The surrogate solvent is added to the device during vacuum assisted distillation to replace the photopolymer solvent being separated and removed from the waste photopolymer fluid. The surrogate solvent maintains the photopolymer resins and rubbers in concentrated solution by coating the acrylic elastomer particles to prevent cross linking and vulcanization, thereby preventing coalescence of the residue as the photopolymer solvent fluid is removed. Even after the residue cools, the residue remains a liquid. Also, by utilizing a low cost surrogate solvent, the economic efficiency of the device is increased due to higher photopolymer solvent recovery. An example of such a device is described in U.S. Pat. No. 5,308,452.
Once the distillation process is completed, it is desirable to remove the concentrated residue from the device as soon as possible. However, a fire hazard exists if the flash point temperature of the concentrated residue is below 140xc2x0 F. As hot concentrated residue is drained from the device, the residue presents a fire hazard due to tribal chain electrical reaction with some prior art devices, particularly when the device is operating at a relatively high distillation temperature. Due to the heat of the residue, the air and vapors proximate to the draining, hot residue expands rapidly and generates static electricity as the gaseous molecules move past one another. Although the device may be grounded, electrical discharge can occur across the gaseous molecules themselves, generating a spark to ignite the vapors and the residue. As a safety precaution, some prior art devices permit the concentrated residue to cool within the device prior to draining. Again, this is undesirable due to the risk of the concentrated residue solidifying in the device, and the device can not renew distillation operations until the device is drained of the concentrated residue.
Thus, there remains a need for a device for separating photopolymer solvent from waste photopolymer fluid which maximizes solvent recovery while producing a coalescable concentrated residue having a flash point temperature in excess of 140xc2x0 F. Accordingly, it is to the provision of such that the present invention is primarily directed.
This invention overcomes the disadvantages of the prior art by providing a modular solvent recovery device that is simple in design and construction, relatively inexpensive to fabricate and easy to use. The modular solvent recovery device is readily transportable and connectable to a conventional plate processor without any modifications to the plate processor. The device includes an enclosure which provides access to the device interior. A frame supports a tank having a solvent section and a waste fluid section. The waste fluid section receives waste photopolymer fluid directly from the plate processor, and because the device is automated, the device is capable of receiving the waste photopolymer fluid on a continuous basis. Recovered solvent is transported directly to the plate processor from the solvent section. A still receives waste photopolymer fluid from the waste fluid section of the tank and distills the waste photopolymer fluid by application of heat and vacuum pressure thereto to separate and recover a desired solvent from the waste photopolymer fluid and reduce the waste photopolymer fluid to a concentrated residue. The device employs a novel flash-point-increasing agent delivery system to supply a flash-point-increasing agent to the concentrated residue in an amount sufficient to raise the flash point temperature of the concentrated residue to a predetermined temperature. This novel process enables the flash point temperature of the concentrated residue to be raised to a temperature that qualifies the concentrated residue, if maintained as a liquid through reduced solvent recovery, to be classified as a Class III residue. Importantly, this novel process permits almost complete recovery of the solvent while maintaining flowability of the coalescing concentrated residue. Further, the concentrated residue can be drained immediately after distillation operations cease without risk of fire due to tribal chain electrical reaction.
The still has a novel manhole device to removably seal a manhole of the still. The manhole device comprises a pivotally and telescopically mounted closure having wheels rotatably mounted thereto. Tracks are mounted to the still to engage the wheels and raise the closure vertically above a manhole of the still upon pivotal movement of the closure.
The modular solvent recovery device utilizes an ultrasonic sensor to detect fluid levels in the tank and residue level in a residue container. A housing is provided to enclose ultrasonic fluid level sensors.
It is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
Other advantages and capabilities of the invention will become apparent from the following description taken in conjunction with the accompanying drawings showing preferred embodiments of the invention.